Spin helices in GaAs quantum wells: Interplay of electron density, spin diffusion, and spin lifetime

TL;DR

This study investigates how electron density influences spin diffusion, lifetime, and polarization in GaAs quantum wells, revealing that optimal spin lifetime occurs at specific electron densities related to statistical transitions, beyond the persistent spin helix condition.

Contribution

It demonstrates that electron density significantly affects spin lifetime and diffusion, emphasizing the importance of scattering rates over the persistent spin helix condition in GaAs quantum wells.

Findings

Longest spin lifetime at electron density near the transition from Boltzmann to Fermi-Dirac statistics

Spin relaxation rate is governed by the spin diffusion coefficient, not just spin-orbit parameters

Electron density impacts spin dynamics more than the balance of Rashba and Dresselhaus effects

Abstract

To establish a correlation between the spin diffusion, the spin lifetime, and the electron density, we study, employing time-resolved magneto-optical Kerr effect microscopy, the spin polarization evolution in low-dimensional GaAs semiconductors hosting two-dimensional electron gases. It is shown that for the establishment of the longest spin-lifetime, the variation of scattering rate with the electron density is of higher importance than the fulfilling of the persistent spin helix condition when the Rashba $\alpha$ and Dresselhaus $\beta$ parameters are balanced. More specifically, regardless of the $\alpha$ and $\beta$ linear dependencies on the electron density, the spin relaxation rate is determined by the spin diffusion coefficient that depends on electron density nonmonotonously. The longest experimental spin-lifetime occurs at an electron density, corresponding to the transition from Boltzmann to Fermi-Dirac statistics, which is several times higher than that when the persistent spin helix is expected. These facts highlight the role the electron density may play when considering applications for spintronic devices.